Question 46

The first operation finds the set of courses taken by student 'SA':

From the given table, student 'SA' is enrolled in courses: CA, CB, CC.
Thus, $T1 = \{\text{CA}, \text{CB}, \text{CC}\}$.

The second operation is relational division:

By definition, $\text{CR} \div T1$ returns all students who are associated with every course in $T1$ (i.e., students who are enrolled in all three courses CA, CB, and CC).

Check each distinct student in relation CR:

• SA: has $\{\text{CA}, \text{CB}, \text{CC}\} \implies$ enrolled in all three $\implies$ Included.
• SB: has $\{\text{CB}, \text{CC}\} \implies$ missing CA $\implies$ Not included.
• SC: has $\{\text{CA}, \text{CB}, \text{CC}\} \implies$ enrolled in all three $\implies$ Included.
• SD: has $\{\text{CA}, \text{CB}, \text{CC}, \text{CD}\} \implies$ contains all three $\implies$ Included.
• SE: has $\{\text{CD}, \text{CA}, \text{CB}\} \implies$ missing CC $\implies$ Not included.
• SF: has $\{\text{CA}, \text{CB}, \text{CC}\} \implies$ enrolled in all three $\implies$ Included.

Therefore, $T2$ contains the 4 students: $\{\text{SA}, \text{SC}, \text{SD}, \text{SF}\}$. The number of rows in $T2$ is 4.